The present invention relates, in general, to electrical interconnects and, more particularly, to interconnect bumps.
Semiconductor manufacturers often form conductive bumps on semiconductor chips to facilitate electrical contact to substrates such as printed circuit boards, Tape Automated Bonding (TAB) substrates, leadframes, etc. Advantages of using conductive bumps include: increased Input and Output (I/O) density, which results in a smaller device xe2x80x9cfootprint,xe2x80x9d increased signal propagation speed due to shorter interconnections, reduced vertical profile, and lower device weight.
Typically, the conductive bumps are formed by depositing a layer of masking or stencil material over the substrate, forming openings in the solder mask, disposing a conductive paste in the openings, and reflowing the conductive paste to form the conductive bumps. A disadvantage of presently available conductive pastes is that voids are formed in the conductive bumps after reflowing the conductive paste. These voids weaken the joints between the conductive bumps and the substrates, which result in reliability problems. In addition, residual flux remains after the reflow step that is difficult to remove. This residual flux reduces the adhesive strength between the conductive bumps and the underfill material and increases the device leakage current.
Accordingly, it would be advantageous to have a conductive paste for making conductive bumps and a method for making conductive bumps having a reduced number of voids. It would be of further advantage to be able to form conductive bumps that can be easily and cost efficiently cleaned after reflow.